For example, a Patent Document 1 discloses an EGR gas control valve (EGRV) as a conventional valve device employed in an EGR system. The EGR system is configured to recirculate a part of exhaust gas from a combustion chamber of an internal combustion engine into an intake air passage. The EGRV controls a quantity of flow of exhaust gas to be recirculated.
The EGRV includes a valve element to control a quantity of flow correspondingly to its opening position. The EGRV further includes a sensor to detect the opening position of the valve element and an actuator to implement a feedback control to manipulate the valve element according to an output signal from the sensor thereby to control a quantity of flow.
[Patent Document 1] Publication of Unexamined Japanese Patent Application No. 2009-2325
It is noted that, a valve device has its own flow characteristic, which is a relation between the opening position of the valve element and the quantity of flow. The flow characteristic have a variation among individual valve devices due to a variation in shapes of components, a variation in assembly of components, a variation in characteristics of sensors, and/or the like. That is, each individual valve device has an error relative to a reference flow characteristic. Therefore, when an open-control method is employed to control a quantity of flow in each valve device with reference to a single predetermined flow characteristic, the quantity of flow may largely vary among individual valve devices. Consequently, accuracy of flow control may become insufficient to increase emission of exhaust gas and/or to decrease fuel efficiency.
It is further noted that, even in a configuration where a feedback control is implemented in the flow control according to an output signal sent from a flow sensor, open control may be still implemented temporarily. Therefore, accuracy of the flow control at the time of the open control is still desired.